An important long range objective of solar energy research is the discovery and development of photoconversion materials, processes, and architectures that can produce solar generated electricity at costs competitive with the cost of electricity generated from fossil fuels such as petroleum, natural gas, or coal. In general, solar electricity systems will require relatively high conversion efficiencies and such systems must be relatively inexpensive to produce to become cost competitive with fossil fuel.
A photovoltaic device, commonly referred to a solar cell or solar panel, is a type of optoelectronic device that converts incident sunlight into electrical current which may then be used to power any type of electrical system or stored in a storage device such as a battery. Semiconductor materials in bulk form currently dominate the field of commercial photovoltaic (PV) power. More sophisticated materials and architectures having higher efficiencies are being developed.
Colloidal Quantum Dots (referred to herein as QDs) are one material being developed for use in solar cells, photovoltaic devices or other optoelectronics. Colloidal QDs are also known as nanocrystals (referred to herein as NCs). QDs and/or NCs are believed to be inherently well suited for the development of relatively inexpensive higher efficiency solar cells for several reasons, including but not limited to observations that QD materials are in certain instances relatively inexpensive and that these materials exhibit an enhanced capacity for multiple exciton generation (MEG).
In particular, the spatial confinement of electrons and holes in QDs and other NCs causes several important effects: (1) e− and h+ pairs are correlated and thus exist as excitons rather than free carriers, (2) the rate of exciton cooling can be slowed because of the formation of discrete electronic states, (3) momentum is not a good quantum number and thus the need to conserve crystal momentum is relaxed and (4) Auger processes are greatly enhanced because of increased e−-h+ Coulomb interaction. Because of these factors it has been observed that the production of multiple e−-h+ pairs (excitons) from high energy photons can be enhanced in QDs compared to bulk semiconductors of the same compositon.
Nonetheless, known solar cells employing a QD active layer typically exhibit relatively low conversion efficiencies. The observed lower conversion efficiencies have many causes. One observed reason for the lower conversion efficiencies observed in QD solar cells is that solar cells fabricated with a QD active layer typically do not exhibit MEG.
The methods and devices disclosed herein are directed toward overcoming one or more of the problems discussed above. The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.